request token returning 401?

[rjgee]

I'm trying to access the api from an Android application. I'm using signpost for authentication. The very first step, GET https://api.500px.com/v1/oauth/request_token, is returning a 401. The consumer key is correct and I can see that signpost generated a signature, nonce, and other oauth headers.

This worked once... however I did not complete the exchange for an access token. Any ideas what I am doing wrong?